I looked on topsecretrecipes.com to see if I could find the Subway cookies. The guy who runs it takes restaurant food, and tries to figure out the recipe and techniques to make it. There were not cookie recipes for Subway, but there was a recipe for Mrs. Field's cookies, which are also really gooey.
On that note, I've really found that it's not so much the recipe, but the cooking time that makes the difference in gooeyness. I take them out of the oven just when they get a little tan around the edges, but still look undone in the middle. They'll carry over bake a little bit on the sheet after you take them out of the oven. Another idea I have is to mix up a batch, but only bake however many you're going to eat at a time, and keep the rest in the freezer. Then you're guaranteed to not have stale, hard cookies.